FIGURE 7.2 Standard wiring convention for 110-V electric power to equipment.

cables properly, even if only for temporary use, and keep them out of aisles and other traffic areas. Install overhead racks and floor channel covers if wires must pass over or under walking areas. Do not intermingle signal and power cables in cable trays or panels. Special care is needed when installing and placing water lines (used, for example, to cool equipment such as flash lamps for lasers) so that they do not leak or produce condensation, which can dampen power cables nearby.

Equipment plugged into an electrical receptacle should include a fuse or other overload protection device to disconnect the circuit if the apparatus fails or is overloaded. This overload protection is particularly useful for equipment likely to be left on and unattended for a long time, such as variable autotransformers (e.g., Variacs and powerstats),2 vacuum pumps, drying ovens, stirring motors, and electronic instruments. If equipment does not contain its own built-in overload protection, modify it to provide such protection or replace it with equipment that does. Overload protection does not protect the trained laboratory personnel from electrocution but does reduce the risk of fire.

7.C.1.3 General Precautions for Working with Electrical Equipment

Laboratory personnel should be certain that all electrical equipment is well maintained, properly located, and safely used. To do this, review the following precautions and make the necessary adjustments prior to working in the laboratory:

   Insulate all electrical equipment properly. Visually inspect all electrical cords monthly, especially in any laboratory where flooding can occur. Keep in mind that rubber-covered cords can be eroded by organic solvents, ozone (produced by ultraviolet lamps), and long-term air oxidation.

   Properly replace all frayed or damaged cords before any further use of the equipment is permitted. Qualified personnel should conduct the replacement.

   Ensure the complete electrical isolation of electrical equipment and power supplies. Enclose all power supplies in a manner that makes accidental contact with power circuits impossible. In every experimental setup, including temporary ones, use suitable barriers or enclosures to protect against accidental contact with electrical circuits.

   Many laboratory locations are classified under fire and electrical codes with a mandate for nonsparking explosion-proof motors and electrical equipment. Areas where large amounts of flammable solvents are in use also require explosion-proof lighting and electrical fixtures. The owners of such facilities are responsible for ensuring that all electrical equipment and fixtures meet these codes and regulations.

   Equip motor-driven electrical equipment used in a laboratory where volatile flammable materials may be present with either nonsparking induction motors that meet Class 1, Division 2, Group C-D electrical standards (Earley, 2008; NFPA, 2008) or air motors instead of series-wound motors that use carbon brushes, such as those generally used in vacuum pumps, mechanical shakers, stirring motors, magnetic stirrers, and rotary evaporators. Do not use variable autotransformers to control the speed of an induction motor. The speed of an induction motor is determined by the AC frequency rather than the voltage. Thus, using a variable autotransformer that controls voltage and not frequency could cause the motor to overheat and presents a fire hazard.


2Commonly known as “variacs,” variable autotransformers are devices that provide a voltage-adjustable output of AC electricity using a constant voltage input (e.g., the wall outlet).

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